Laboratory Thermometers

Laboratory thermometers are used to measure temperatures or temperature changes with a high degree of precision. They are made of metal or glass and strengthened through processes such as thermal tempering or annealing. Several types of laboratory thermometers are commonly available. Liquid-in-glass thermometers are made of sealed glass and contain a fluid, usually mercury or red alcohol, whose volume changes relative to its temperature. Bimetallic strip thermometers include two different metals that are bonded together and expand at different rates as they warm up. Often, long bimetallic strips are wound into a coil and used with a dial. Electronic devices such as thermistors measure changes in electrical resistance and convert them to changes in temperature. Infrared thermometers are non-contact devices that convert infrared (IR) energy to an electrical signal that can be displayed in units of temperature. Other specialized or proprietary products are also available.

Laboratory thermometers measure temperatures in degrees Fahrenheit (F) or degrees Celsius (C). Graduated scalar divisions or test points determine the accuracy with which users can read each type of device. Typically, display numbers are etched or printed on the thermometer’s housing. With some devices, permanent pigmentation of graduations is used to improve readability. Features such as clip-on magnifiers help users read numbers on more detailed scales. Some laboratory thermometers can be fully immersed in the media being measured. Others can withstand only partial immersion. Devices encapsulated with polytetrafluoroethylene (PTFE) are suitable for monitoring acids or other hazardous materials. Teflon^®, a registered trademark of DuPont, is a common, proprietary form of PTFE. Laboratory thermometers with a protective metal sheath and no-roll cap are commonly available. 

Organizations such as the National Institute of Standards and Technology (NIST) and the American Society of Testing and Materials (ASTM) calibrate laboratory thermometers and provide traceability. NIST provides calibration services for a variety of laboratory thermometers that cover a temperature range from -196° C to 550° C (-321° F to 1022° F). Submitted devices must pass a preliminary examination for fineness and uniformity of graduation as well as freedom from moisture, gas bubbles, and cracks. The thermometers to be calibrated are placed in a constant temperature bath along with an NIST-calibrated standard platinum resistance thermometer (SPRT) that is traceable to the International Temperature Scale of 1990 (ITS–90). Special tests may also be conducted on industrial-grade platinum resistance thermometers, digital thermometers, and thermistors. ASTM-certified laboratory thermometers must also pass rigorous testing requirements.

• Stem Conduction and Light Piping in ITS-90 Fixed Point Cell Assemblies at a UKAS Laboratory
  Standard Platinum Resistance Thermometers (SPRTs) with length-below-handle of only 480mm are regularly submitted for calibration at ITS-90 fixed points from -200 °C to +660 °C. The length of the...
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Part Numbers for Laboratory Thermometers